A photovoltaic system (or PV system) is a system which uses many solar cells usually in the form of one or more solar panels to convert sunlight into electricity. It can comprise multiple components, including photovoltaic modules, mechanical and electrical connections and mountings and means of regulating and/or modifying the electrical output as well as means to track the sun. The efficiency of the solar system is reduced during dynamic conditions by time-dependent effects. The efficiency of today's power circuits is high, although the overall efficiency is strongly affected from varying factors such as partial shading. In rooftop applications these problems become more important. Known configurations that are used in today's systems are not dealing with these problems effectively during operation, i.e. at the run-time of the system. Maximum power point tracking (MPPT) is a technique that solar inverters use to get the maximum possible power from the PV system. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces a non-linear output efficiency known as the I-V curve. It is the purpose of the MPPT system to sample the output of the cells and apply a resistance (load) to obtain maximum power for any given environmental conditions. Essentially, this defines the current that the inverter should draw from the PV system in order to get the maximum possible power. The MPP tracker is vital for a large number of modules, making the module mismatching a crucial factor. Even when the control is decentralized at the module level, the efficiency is further reduced and reliability issues make these configurations inefficient.
WO2005/112551 describes an auxiliary power source connected to each PV module of series connected strings. In case of partial shading, this source supplies the necessary power in order to prevent a temporary shut-down. The MPPT controls the switches of the power source.
Modules which are widely used nowadays are uniform. All cells of commercial modules are permanently connected in series and the controls of the system are mainly situated in the central or local converters. As the excitation of the PV system is not uniform (e.g. non-uniform irradiation, and/or temperature), a small group of cells can cause the module to operate well below optimum. In the case of total destruction or shading of some cells, the whole module is potentially disconnected from the system leading to a significant loss of power. In the literature, several proposals are introduced which use more controls than purely in the converter. They focus mainly on adding local control at the module level. Dynamic interconnections of the cells within the module have been introduced as well. Known module configurations are however uniform. Some studies propose switches between the cells, enabling all possible connections of a solar cell with neighboring cells in a uniform way. This number of connections leads to a large overhead in terms of both long wires and many switches. This is not considered acceptable from a fabrication cost point of view. There has been little effort to connect cells which are not neighboring. Known configurations exhibit uniform topologies with symmetry rules.
US20090079412 describes an apparatus and method controlling the output of a PV array which disclose that a high enough output voltage can be obtained by uniformly switching N parallel connected cell strings into N/M parallel connected groups of M times longer cell strings. Every MPTT or controller is purely locally driven, even when it is conceptually used in an intra-module manner. It is noticeable in the array that there are long conductors which span from one end of strings of cells to the other.